Digital subscriber line (DSL) technologies are utilized to supply high speed data over twisted pair conductors. Current DSL standards may comprise asymmetric DSL (ADSL, ADSL2 and ADSL2+), very-high-bit-rate DSL (VDSL and VDSL2), and integrated services digital network (ISDN). These technologies may use baseband transmission in conjunction with plain old telephone service (POTS). DSL signals may occupy higher frequency bands while the POTS signals may be transmitted over frequency bands below 4 kilohertz (KHz). The DSL and POTS signals may be split and coupled through a splitter to the corresponding receiver and network, respectively.
Discrete multi-tone modulation (DMT) may be implemented in DSL systems. DSL access multiplexer (DSLAM) equipment may offer multi-port access and support to different DSL technologies. ADSL/ADSL2 and VDSL2 standards may employ frequency division duplexing (FDD), in which downstream (DS) and upstream (US) transmission occurs simultaneously at two different frequency bands. However, these standards may suffer from issues with near-end crosstalk (NEXT) and echo during transmission.
Alternatively, time-division duplex (TDD) systems may be utilized, in which US and DS transmissions may occur in different time intervals. DS signals of different lines may be transmitted at the same time since all the transceiver units are all located and controlled at the central office side. However, US signals may be transmitted at varying times and should be aligned properly to facilitate crosstalk elimination at central office or operator-side transceivers. Timing offsets between various signals arriving from the customer premises may detrimentally affect crosstalk cancellation. Thus, there is a need to improve the alignment of US symbols as seen at operator-side equipment in order to enhance crosstalk cancellation.